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Circle of Circles

This talk will highlight some interesting theorems regarding sets of circles in the plane, including (1) Descartes's Four-Circles Theorem, which in a simple formula con-
nects the curvatures of four circles that are mutually tangent, and (2) Monge's Problem and the concept of the Radical Center (or Power Center) of three circles, which leads

to the Spieker Point of a triangle as the Radical Center of its three excircles, an obscure "special point" of a triangle that has such wondrous properties it should be better
known!